This invention relates in general to medical apparatus and more particularly, to medical apparatus especially for use in connection with taking internal pressure measurements of a patient.
In the management of critically ill patients, it has become common to monitor, on a continuous or regular basis, various pressures in the vessels of the patient. For example, monitoring pulmonary artery and pulmonary capillary wedge pressures with a catheter (such as the one sold by American Edwards Laboratories under the trade designation SWAN-GANZ) to detect left ventricular failure is a standard procedure in many hospitals for management of critically ill patients. The proximal end of these catheters is placed in the vessel of the patient at the point where the pressure is to be measured. Catheters used in this way have a lumen which extends from a predetermined point on the catheter such as the end thereof back to the distal end of the catheter where it is connected to a pressure transducer. These pressure transducers are available from a variety of sources and include a strain gauge which converts the pressure present on a diaphragm of the transducer into an electrical signal for standard monitoring equipment. These pressure transducers are commonly mounted at a fixed vertical position on a movable structure near the patient, such as an IV pole. It is necessary for the transducer to be fixed vertically because otherwise movement of the transducer up or down the pole would result in a differing output from the transducer caused by the varying head of the fluid in the catheter. As can be appreciated, in the care of critically ill patients, it is desirable that the pressure readings taken by such transducers be consistent, accurate, and reliable.
Even though the transducer is fixed vertically with respect to the IV pole, the patient is not fixed with respect to the transducer. For example, the hospital bed in which the patient reclines may be moved upwardly or downwardly by a medical care professional for any number of reasons. In addition, mere movement of the patient on the bed can result in varying and inconsistent readings at the pressure transducer. For this reason, the vertical position of the patient with respect to the transducer must be kept fixed or at least periodically readjusted. However, since the transducer is spaced some distance from the patient, fixing of the relative vertical positions is not a simple task. At present, a carpenter's level of considerable length (three feet or more) is physically placed between the transducer and a predetermined point on the body of the patient each time readjustment is desired. The patient or the transducer is then moved vertically to provide the desired predetermined vertical spacing between the two.
The IV pole on which the transducer is mounted can be very crowded when the transducer is being used in connection with a patient in critical care. Thus, it is sometimes inconvenient to accurately place the carpenter's level in the proper position adjacent the pressure transducer to get an accurate measurement of the relative vertical positions of the transducer and the patient. Moreover, if the spacing between the patient and the pressure transducer is longer than the carpenter's level used to level the patient with respect to the transducer, the leveling will be only approximate. Conversely, if the distance is much shorter than the level, it could be necessary to either move the IV pole further away from the patient, or to have the carpenter's level extend past the pressure transducer. In any case, the large size of the carpenter's level makes it inconvenient to use in the confines of a critical care room.